1. Field of the Invention
This invention relates to metal oxide crystals. More specifically, the invention discloses a method using alkaline earth fluxes for generating new and difficult-to-grow metal oxide crystals.
2. Brief Description of the Related Art
Discovery and Growth of Crystalline Materials (DGCM) has been recently identified as key area for materials research (Frontiers in Crystalline Matter: From Discovery to Technology; National Research Council, Washington, D.C., 2009). Single crystals are needed to fully characterize physical properties of materials with possible semiconductor applications, optical materials, energy conversions materials and detectors. Original and unique growth processes will spearhead discovery efforts by exploring specialized synthesis pathways to both new and desirable single crystalline materials.
Traditional growth processes do not possess the exploratory edge of a new method that develops original techniques into reliable, reproducible processes that can be further applied to numerous systems. The current state of the art for growth of metal oxide single crystals often involves temperatures in excess of 1000° C., and occasionally high pressure. In the past, p-block metal fluxes have been applied almost exclusively to the growth of intermetallic and other non-oxide phases (Kanatzidis, M. G., Pöttgen, R. and Jeitschko, W. The metal flux: A preparative tool for the exploration of intermetallic compounds. Angew. Chem. Int. Ed. 44, 6996-7023 (2005)), such as the clathrate-type system Ba8Al16Ge30 (Christensen, M., Johnsen, S. and Iversen, B. B. Thermoelectric clathrates of type I. Chem. Mater. 19, 4896-4905 (2007)), or intermetallic phases of the ThCr2Si2-type (Joshi, D. A., Nagalakshmi, R., Kulkarni, R., Dhar, S. K. and Thamizhavel, A. Crystal growth and anisotropic magnetic properties of RAg2Ge2 (R=Pr, Nd and Sm) single crystals. Physica B—Cond. Matter 404, 2988-2991 (2009); Wang, H. F., Cai, K. F., Li, H., Wang, L. and Zhou, C. W. Synthesis and thermoelectric properties of BaMn2Sb2 single crystals. J. Alloys Comp. 477, 519-522 (2009); Singh, Y., Lee, Y., Nandi, S., Kreyssig, A., Ellern, A., Das, S., Nath, R., Harmon, B. N., Goldman, A. I. and Johnston, D. C. Single-crystal growth and physical properties of the layered arsenide BaRh2As2. Phys. Rev. B 78, 104512 (2008)). In particular, tin fluxes have been used on many occasions to grow complex poly-phosphide phases containing extended phosphorus-phosphorus bonding (Jeitschko, W., Foecker, A. J., Paschke, D., Dewalsky, M. V., Evers, C. B. H., Kunnen, B., Lang, A., Kotzyba, G., Rodewald, U. C. and Moller, M. H. Crystal structure and properties of some filled and unfilled skutterudites: GdFe4P12, SmFe4P12, NdFe4As12, Eu0.54Co4Sb12, Fe0.5Ni0.5P3, CoP3, and NiP3. Z. Anorg. Allg. Chem. 626, 1112-1120 (2000); Jeitschko, W., Wallinda, J., Dewalsky, M. V. and Wortmann, U. Preparation, Properties, and Structure of the Polyphosphides VNi4P16, NbNi4P16, and WNi4P16. Z. Naturforschung B 48, 1774-1780 (1993); Jeitschko, W., Brink, R. and Pollmeier, P. G. The Ternary Uranium Transition-Metal Phosphides UV5P3, UCr5P3, and UMn5P3. Z. Naturforschung B 48, 52-57 (1993)), as well as tetrelides, pnictides, such as the thermoelectric materials Yb14MnSb11 (Brown, S. R., Kauzlarich, S. M., Gascoin, F. and Snyder, G. J. Yb14MnSb11: New High Efficiency Thermoelectric Material for Power Generation. Chem. Mater. 18, 1873-1877 (2006)), the superconducting phases Ba1-xKxFe2As2 (Ni, N., Bud'ko, S. L., Kreyssig, A., Nandi, S., Rustan, G. E., Goldman, A. I., Gupta, S., Corbett, J. D., Kracher, A. and Canfield, P. C. Anisotropic thermodynamic and transport properties of single-crystalline Ba1-xKxFe2As2 (x=0 and 0.45). Phys. Rev. B 78, 014507 (2008)) and LaNiPO (Tegel, M., Bichler, D. and Johrendt, D. Synthesis, crystal structure and superconductivity of LaNiPO. Solid State Sci. 10, 193-197 (2008)), to mention just a few.
In contrast, flux growth of oxides normally involves the use of oxide or salt fluxes. As an example, garnet growth from PbO—B2O3 fluxes has been optimized to give large single crystals (Parker, S. G. and Chang, C. T. M. Influence of Growth-Conditions on the Properties of Small Diameter Bubble Garnet-Films Grown from PbO—B2O3 Flux. J. Cryst. Growth 55, 438-446 (1981)). Other examples include the LiCoO2 battery electrode material synthesized from Li2O/LiCl flux and highly reduced alkaline earth niobate crystals from borate fluxes. (Akimoto, J., Gotoh, Y. and Oosawa, Y. Synthesis and Structure Refinement of LiCoO2 Single Crystals. J. Solid State Chem. 141, 298-302 (1998); Hessen, B., Sunshine, S. A., Siegrist, T. and Jimenez, R. Crystallization of reduced strontium and barium niobate perovskites from borate fluxes. Mat. Res. Bull. 26, 85-90 (1991)).
3. Problems to be Solved by the Invention
There lacks a process that generates a favorable environment to produce oxide single crystals at low temperatures and pressures. The prior art lacks the methodology to use temperatures below 1000° C. and not apply pressure. A new, less expensive or faster method of growing metal oxides will have significant value to industry and government, while providing an avenue for potential new discoveries.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the field of this invention how the shortcomings of the prior art could be overcome.